Final answer:
Children commonly need to wear a PFD on boats under 26 feet long, usually if they are under the age of 13, but exact age requirements can vary by region.
Step-by-step explanation:
The question of what age children must wear a Personal Flotation Device (PFD) while on a boat under 26 feet long depends on the specific regulations that are established by coast guards or marine authorities in different regions. Generally, it is a common safety practice that children under a certain age are required to wear life jackets or PFDs at all times while aboard small boats. While each country or state may have its own specific rules, a common regulation is that children under the age of 13 must wear a PFD on small boats.